Progression through the cell cycle is a highly ordered process, and yet little is known about its molecular mechanism. Recent studies from numerous labs have begun to unveil the components of this complex regulatory network. I have previously identified one such protein, called Pds1p, in the budding yeast. This protein acts as a negative regulator of progression through mitosis, and it appears to be involved both in normal cell cycle progression as well as in the DNA damage checkpoint pathway. I intend to study the molecular events that are involved in the regulation of cell cycle progression through mitosis, under both normal and adverse conditions. This will be done via genetic and biochemical methodologies, using budding yeast as a model system. The Pds1p protein will be examined for its molecular function as a negative regulator, and it will serve as a handle for identifying additional proteins that are involved in the process. These studies are expected to shed light on the regulation of cell cycle progression not only in yeast, but in higher eukaryotes as well.